In the past, corrosion of metal surfaces in contact with motor fuels such as gasoline was not much of a problem because such hydrocarbon fuels were non-corrosive and served to limit surface contact with water and moisture. With the advent of fuels partly containing alcohols such as gasohol or straight alcohol fuels, corrosion has become a major problem. Because of their higher water content and acidic impurities, alcohol fuels provide an environment conducive to the oxidation of uncoated ferrous surfaces by dissolved oxygen gas. Acidic contaminants contained in the fuel such as formic and acetic acid can arise during processing or from oxidation of the fuel during storage.
It is known from U.S. Pat. No(s). 4,509,951, 4,511,367, 4,511,368 and 4,531,948 that the combination of a carboxylic acid compound such as dimers and trimers of polyunsaturated fatty acids or alkenyl succinic acid with a nitrogen containing compound such as a polyisobutenyl (PIB) succinimide or a substituted imidazoline is effective as a corrosion inhibitor for alcohol-type motor fuels.
In addition, several proprietary formulations of corrosion inhibitors for alcohol motor fuels are available for sale at the retail level. These include ALCOOL (Shell Oil), GRAND PRIX and PROAL (Bardahl) which are widely used in Brazil.
It has now been found in accordance with the present invention that the combination of an alkenyl succinimide prepared with a mixture of amines and a substituted imidazoline provides improved corrosion inhibiting properties to alcohol-type motor fuel.
The alkenyl succinimide co-additive of this invention, more fully described hereafter, is also a known compound which heretofore has found use, for example, in motor fuel compositions to prevent carburetor deposits and fuel injector clogging as disclosed in U.S. Pat. No(s). 4,863,487 and 4,895,578.